500 5-Minute Writing Excercises by Nadiyah Abdul-Khaliq
Price: $5.99 USD. 7690 words.
Published on November 17, 2012. .
There are no rules to use this book. Just relax, commit to an exercise, and set that clock to five minutes. Grammar is not the most important part of an exercise. The point is that you get used to just writing whatever comes to mind and seeing where the story takes you.
Do take chances and experiment with exercises, reverse them, manipulate them.